The US secretary of state said on Wednesday there was a strong chance Russian opposition leader Alexei Navalny's poisoning was ordered by senior officials in Moscow.
Navalny, the most visible critic of Vladimir Putin within Russia, fell violently ill last month as he took a flight in Siberia. He was flown for treatment to Germany, where doctors said he was poisoned.
"I think people all around the world see this kind of activity for what it is," Mike Pompeo said in a radio interview.
"And when they see the effort to poison a dissident, and they recognise that there is a substantial chance that this actually came from senior Russian officials, I think this is not good for the Russian people," he told conservative host Ben Shapiro.
Mr Pompeo reiterated that the United States and its European allies all wanted Russia to "hold those responsible for this accountable" and said Washington would also try to identify the perpetrators.
"It's something that we'll take a look at, we'll evaluate, and we'll make sure we do our part to do whatever we can to reduce the risk that things like this happen again."
Mr Pompeo's remarks come despite President Donald Trump's claim last week that he had seen no proof that Mr Navalny was poisoned.
Mr Trump has sought warmer relations with Mr Putin, although his administration has still pushed sanctions over Ukraine and other concerns.
Three activists linked to the poisoned Russian opposition leader Alexei Navalny were taken ill on Tuesday after attackers hurled a jar containing an unknown liquid into their office in Siberia.